Running SQL from memory faster than SSD?

Which is faster SSD or Memory

DRAM is faster than NAND flash. A RAM access is on the order of 100 ns, while a SSD random read around 16,000 ns. Latency Numbers Every Programmer Should Know

You need to do a systematic analysis of what is happening and why. Do not change things merely because you heard something secondhand about another system. Find what the problem is on this system.

Fortunately DBMS systems tend to have performance tools. Oracle and other RDBMS have EXPLAIN PLAN to show full scans and other inefficiencies. Queries can perform terribly even with indices. There are also system performance reports like Oracle AWR to find bottlenecks. If you wish to inquire further about DB performance you can also ask our sister site, https://dba.stackexchange.com/